Inexorable advances in consumer electronics have led to affordable digital video devices capable of rendering crisp images with high fidelity audio. The emergence of digital video devices with recording capability represents a significant threat to content providers, since the content of high quality digital programs can be easily duplicated. The motion picture, film and video industry estimate that substantial sums have been lost annually due to unauthorized duplication. Such unauthorized duplication deprives the rightful owners or distributors of program content of their income and reduces their incentive to produce new movies and videos. Thus, the protection of program contents especially high definition digital program content, from unauthorized copying is an important problem facing the consumer electronics industry.
Due to the need for a secure transmission of programs, a number of video encoding or scrambling techniques have been developed to provide control over potential recipients and to prevent unauthorized use of received transmissions. For instance, to block reception by non-subscribers, television subscription networks typically encode or scramble the distributed television signals, thereby defeating acceptable display of those television signals by non-subscribers who do not have the proper decoders or descramblers.
However, an authorized subscriber may simply connect a video recorder to his decoder to record for subsequent and repeated viewing a desired program that is distributed over the subscription network. Such recording for later viewing decreases the market interest in subsequent distribution of that program over the subscription network. For instance, “pay per view” broadcasts contemplate a once-only distribution of video programming such as first run motion pictures, popular sporting events and special entertainment events to subscribers who are charged a one-time fee to receive that particular program. Such one-time broadcasting is quite sensitive to unauthorized reproductions which erode the value of the content of the pay-per-view transmission.
Since the scrambling or encoding of the video signal cannot prevent a paying subscriber from recording the program, it is desired that the video signal be modified so that the subscriber can view the program, but the operation of recording equipment should be defeated or tightly controlled to avoid unauthorized recording.
Traditionally, with monitors or display devices that accept analog input signals, methods for making the video signal non-recordable have relied upon adjusting an automatic gain control (AGC) circuit normally included in a videotape recorder. Other techniques for modifying the video signal to prevent its recording or reproduction rely on the relative sensitivity of a vertical sync detection circuit normally provided in videotape recorders. The removal of a portion of the pulses intended for a vertical blanking interval causes a vertical synchronizing detector included in most videotape recorders to be unable to detect those vertical sync pulses, resulting in a loss of control information needed for the proper operation of the videotape recorder.
The advent of digital video recorders that accept high definition analog video inputs has necessitated new solutions for protecting the high definition content. Methods have been developed for encrypting digital data for transmission over high speed digital interfaces, such as IEEE-1394. However, there presently is not a cost-effective digital transmission interface for transmitting uncompressed high definition digital video for consumer applications which require transmission rates of greater than 1 Gigabit/second. For example, the fastest current IEEE-1394 interface standard supports transmission rates of less than 400 Megabits/second. Using compressed bitstreams to transfer the digital data from the set top box to the receiver is problematic because the transmitter needs a high definition Motion Pictures Experts Group (MPEG) encoder to handle locally generated video information such as on screen displays or electronic program guides. Additionally, high definition MPEG encoders are not cost effective for consumer applications.